Atmospheric Ammonia Affects Myofiber Development and Lipid Metabolism in Growing Pig Muscle

Multi-omics reveal the effects and regulatory mechanism of dietary neutral detergent fiber supplementation on carcass characteristics, amino acid profiles, and meat quality of finishing pigs

This study aimed to reveal the effects and regulatory mechanism of dietary NDF on the performance of pigs by multi-omics analysis. Results showed that 16 % dietary NDF significantly improved meat quality, increased flavor amino acid content, and reduced backfat thickness and the feed-to-gain ratio. 16S rDNA sequencing showed that 16 % NDF significantly increased the abundance of Akkermansia, Lachnoclostridium, and Ruminococcus. Transcript analysis showed that genes related to muscle development and lipid metabolism were significantly modified. Metabonomic analysis showed that 16 % NDF significantly increased amino and fatty acid related metabolites. Correlation analysis suggested that 16 % NDF treatment may alter the gut microbiota and metabolites, regulate the expression of genes related to lipid and amino metabolism, and ultimately affect the flavor and performance of pigs. This study provides a novel understanding about the effect and regulatory mechanism of NDF supplements on the finishing pigs and a relevant reference for the improvement of diet formulation.

Advances in the discovery of genetic elements underlying longissimus dorsi muscle growth and development in the pig

As a major source of protein in human diets, pig meat plays a crucial role in ensuring global food security. Key determinants of meat production refer to the chemical and physical compositions or characteristics of muscle fibers, such as the number, hypertrophy potential, fiber-type conversion and intramuscular fat deposition. However, the growth and formation of muscle fibers comprises a complex process under spatio-temporal regulation, that is, the intermingled and concomitant proliferation, differentiation, migration and fusion of myoblasts. Recently, with the fast and continuous development of next-generation sequencing technology, the integration of quantitative trait loci mapping with genome-wide association studies (GWAS) has greatly helped animal geneticists to discover and explore thousands of functional or causal genetic elements underlying muscle growth and development. However, owing to the underlying complex molecular mechanisms, challenges to in-depth understanding and utilization remain, and the cost of large-scale sequencing, which requires integrated analyses of high-throughput omics data, is high. In this review, we mainly elaborate on research advances in integrative analyses (e.g. GWAS, omics) for identifying functional genes or genomic elements for longissimus dorsi muscle growth and development for different pig breeds, describing several successful transcriptome analyses and functional genomics cases, in an attempt to provide some perspective on the future functional annotation of genetic elements for muscle growth and development in pigs.

Excessive ammonia inhalation causes liver damage and dysfunction by altering gene networks associated with oxidative stress and immune function

Ammonia (NH₃) is a major gaseous pollutant in livestock production and has adverse effects on production, health and welfare of animals. The liver is one of the target organs of NH₃, and excessive NH₃ inhalation can induce liver damage. However, the toxicity assessment of NH₃ on pig liver and its mechanism have not been reported yet. Recently, transcriptome analysis has become a major method to study the toxic mechanism of pollutants in environmental toxicology. Therefore, in the present study, we examined the effects of excessive NH₃ inhalation on the liver of fattening pig through chemical analysis, ELISA, transcriptome analysis and real-time quantitative PCR (qRT-PCR). Our results showed that the transcriptome analysis database of fattening pig liver under excessive NH₃ exposure, and 449 differentially expressed genes (DEGs) (including 181 up-regulated DEGs and 168 down-regulated DEGs) were found. Some genes associated with the 3 Gene Ontology (GO) terms (liver function, immune, antioxidant defense) were validated by quantitative real-time PCR. In addition, the activities of GPT and GOT in NH₃ group were significantly increased by 63.5% and 37.4% (P < 0.05), respectively. Our results indicated that NH₃ exposure could cause changes in transcriptional profiles and liver function, and induce liver damage in fattening pigs through oxidative stress and immune dysfunction. Our study results not only provide a new perspective for the toxicity assessment of NH₃, but also enrich the toxicological mechanism of NH₃.

Effects of ammonia on growth performance, lipid metabolism and cecal microbial community of rabbits

This study was designed to investigate the effect of ammonia on growth performance, lipid metabolism and intestinal flora of rabbits. A total of 150 female IRA rabbits (35-days-old) were randomly divided into three groups including 0 ppm (CG), 10 ppm (LAC) and 30 ppm ammonia (HAC) groups for a period of 28 days. The average daily weight gain (ADG) of rabbits was significantly reduced in LAC (-17.11%; p < 0.001) and HAC groups (-17.46%; p < 0.001) as compared with the CG. Serum concentration of high density lipoprotein (HDL) and glucose (Glu) were increased in LAC (+80.95%; +45.99; p < 0.05) and HAC groups (+219.05%; +45.89; p < 0.001), while apolipoprotein A1 (apoA1) was decreased in LAC (-58.49%; p < 0.001) and HAC groups (-36.92%; p < 0.001). The structural integrity of cecum was damaged, and the thickness of mucosa and serosa were significantly decreased in LAC and HAC. The acetate, butyrate and propionate level of cecal chyme were reduced in HAC group (-21.67%; -19.82%; -30.81%; p < 0.05). Microbial diversity and burden of Firmicutes were significantly decreased, while that of pathogenic bacteria, such as Bacteroidetes, Clostridium and Proteobacteria were increased in ammonia treated groups. Spearman's correlation confirmed that burden of Ruminococcaceae_NK4A214_group showed significantly negative correlation with acetic acid (r = -0.67; p < 0.001) while Barnesiellaceae_unclassified showed significantly positive correlation with propionic acid (r = 0.50; p < 0.001). In conclusion, ammonia treatment was responsible for an imbalance of intestinal flora, which affected lipid metabolism and damaged intestinal barrier of rabbits, resulting in low growth performance due to lipid metabolism dysfunction.

Exposure to High Aerial Ammonia Causes Hindgut Dysbiotic Microbiota and Alterations of Microbiota-Derived Metabolites in Growing Pigs

Ammonia, an atmospheric pollutant in the air, jeopardizes immune function, and perturbs metabolism, especially lipid metabolism, in human and animals. The roles of intestinal microbiota and its metabolites in maintaining or regulating immune function and metabolism are irreplaceable. Therefore, this study aimed to investigate how aerial ammonia exposure influences hindgut microbiota and its metabolites in a pig model. Twelve growing pigs were treated with or without aerial ammonia (35 mg/m³) for 25 days, and then microbial diversity and microbiota-derived metabolites were measured. The results demonstrated a decreasing trend in leptin (p = 0.0898) and reduced high-density lipoprotein cholesterol (HDL-C, p = 0.0006) in serum after ammonia exposure. Besides, an upward trend in hyocholic acid (HCA), lithocholic acid (LCA), hyodeoxycholic acid (HDCA) (p < 0.1); a downward trend in tauro-deoxycholic acid (TDCA, p < 0.1); and a reduced tauro-HDCA (THDCA, p < 0.05) level were found in the serum bile acid (BA) profiles after ammonia exposure. Ammonia exposure notably raised microbial alpha-diversity with higher Sobs, Shannon, or ACE index in the cecum or colon and the Chao index in the cecum (p < 0.05) and clearly exhibited a distinct microbial cluster in hindgut indicated by principal coordinate analysis (p < 0.01), indicating that ammonia exposure induced alterations of microbial community structure and composition in the hindgut. Further analysis displayed that ammonia exposure increased the number of potentially harmful bacteria, such as Negativibacillus, Alloprevotella, or Lachnospira, and decreased the number of beneficial bacteria, such as Akkermansia or Clostridium_sensu_stricto_1, in the hindgut (FDR < 0.05). Analysis of microbiota-derived metabolites in the hindgut showed that ammonia exposure increased acetate and decreased isobutyrate or isovalerate in the cecum or colon, respectively (p < 0.05). Unlike the alteration of serum BA profiles, cecal BA data showed that high ammonia exposure had a downward trend in cholic acid (CA), HCA, and LCA (p < 0.1); a downward trend in deoxycholic acid (DCA) and HDCA (p < 0.05); and an upward trend in glycol-chenodeoxycholic acid (GCDCA, p < 0.05). Mantel test and correlation analysis revealed associations between microbiota-derived metabolites and ammonia exposure-responsive cecal bacteria. Collectively, the findings illustrated that high ammonia exposure induced the dysbiotic microbiota in the hindgut, thereby affecting the production of microbiota-derived short-chain fatty acids and BAs, which play a pivotal role in the modulation of host systematic metabolism.

High ammonia exposure regulates lipid metabolism in the pig skeletal muscle via mTOR pathway

Ambient ammonia exposure has been known to perturb lipid metabolism in farm animals, but the underlying mechanism is unclear. The current study was conducted to investigate how ambient ammonia exposure influences lipid metabolism in the pig model. Twelve pigs were randomly divided into two groups, either exposed to 0 or 35 mg/m³ atmospheric ammonia for 25 days. Serum ammonia remained unchanged (p > 0.05), but increased serum urea concentration was found (p < 0.05) after ammonia exposure. Ammonia exposure also caused an increased C18:0, C18:2n6c, C18:3n6, C18:3n3, C20:0, C20:2, C20:3n6, C20:3n3, C22:0 concentrations and fat content in the longissimus dorsi muscle (p < 0.05), and also serum total triglyceride (p = 0.0294) and ApoB (p = 0.0061) contents. Analysis of serum free amino acids profile revealed that concentrations of ornithine, tyrosine, asparagine, histidine, phenylalanine, leucine, isoleucine, glutamine and valine were significantly increased in the pigs exposed to 35 mg/m³ ammonia (p < 0.05). RNA-Seq analysis showed that genes encoding enzymes involved in lipid synthesis (FASN, SCD and FADS1) and uptake (LDLR) were up-regulated, whereas genes related to lipolysis (PNPLA4, ANGPTL4 and CEL), transport (CPT1A, CPT1B and CPT2) and β-oxidation (ACADL, ACADVL, UCP2 and UCP3) were down-regulated. Furthermore, exposure to 35 mg/m³ atmospheric ammonia increased expression of mTOR (p = 0.0377) and its downstream P70S6K (p = 0.0139) and p-P70S6K (p = 0.0431), but decreased AMPK (p < 0.0001) and p-AMPK (p = 0.0071) in the longissimus dorsi muscle. In conclusion, high concentration of atmospheric ammonia exposure greatly interferes with amino acid metabolism, resulting in increased BCAAs and aromatic amino acids. The increased BCAAs production can up-regulate lipid synthesis and down-regulate β-oxidation by activating mTOR signaling and inhibiting AMPK signaling.